This invention relates to methods and machines for screeding that is, spreading, distributing and smoothing and/or leveling placed and/or poured, uncured concrete or like loose, spreadable material such as sand and gravel, or relatively viscous, fluid materials. More particularly, the invention concerns an apparatus and method for screeding such materials without the use or need for prepositioned guides or rails, especially rail guided paving or screeding machines such as slip-form pavers. The invention is an improvement of an earlier apparatus and method for screeding such materials with a device positioned either adjacent the uncured concrete or driven through the uncured concrete while screeding.
The present invention is an improved version of the screeding apparatus and method of U.S. Pat. No. 4,655,633 assigned to the assignees of the present invention. In the device and method of U.S. Pat. No. 4,655,633, a self-propelled apparatus includes a steerable, self-propelled frame, a cantilevered boom, and an auger-type, vibratory screed mounted on the boom for spreading and smoothing the concrete as the screed was moved toward the vehicle. The elevation of the screed is adjusted automatically by a screed control assembly relative to a laser beacon reference plane positioned off the apparatus such that the finished height of the concrete or other material was accurately controlled within close tolerances. The vibratory screed of U.S. Pat. No. 4,655,633 also includes a rotatable auger for spreading the concrete or other material laterally with respect to the direction of movement of the screed, as well as a strike-off member for engaging the concrete behind the auger, both of which were vibrated by a screed vibration assembly on the same support.
Other screed assemblies have included striker blades spaced in front of screed vibration assemblies including certain assemblies used with the apparatus of U.S. Pat. No. 4,655,633, and others such as those shown in U.S. Pat. Nos. 3,541,932 and 3,907,451. The structures of the latter two patents also incorporate augers positioned in front of the striker and screed vibration assemblies. It has been found that such prior devices tended to push concrete in front of the blade or striker. The buildup of concrete in front of the striker blade exerted a horizontal force on the screed assembly, tending to deflect the screed and raise the trailing vibratory screed portion out of the concrete surface. This caused tearing of the surface and consequent roughness because of the lack of smoothing with the vibratory assembly. Hence, it was necessary in many cases to rescreed the same area multiple times thereby increasing the cost and expense for finishing the concrete.
In another aspect of U.S. Pat. No. 4,655,633, the striker member and auger were simultaneously vibrated in unison by a screed vibrating assembly. However, such simultaneous vibration of all parts of the screed assembly contacting the concrete tended to produce roughness and prevent fine, precisely controlled grading or leveling of the concrete areas.
Further, the screed assembly of U.S. Pat. No. 4,655,633 was carried on a truss-type boom assembly of fixed length which, although capable of being extended or retracted, normally protruded from the operator platform of the apparatus. In close quarters in smaller buildings where concrete was being installed, the fixed length boom created problems in maneuvering the screeding apparatus from one area to another, as well as preventing complete withdrawal of the boom and screed assembly to a position close to the screeding apparatus. This prevented maximum efficiency in using the apparatus in such small areas.
Accordingly, the present invention was principally devised to improve the placement and/or finishing of both large and small poured concrete areas by improving the efficiency of the contact of the screeding assembly with the concrete or other material to be spread during screeding operations, and by coupling the screeding assembly with a support boom which could be more easily extended and retracted, especially in confined areas, thereby making the apparatus more easily operated.